The increasingly growing demand for dynamo-electric machines accounts for the acute interest of specialists in the problem of finding more effective ways of manufacturing coil groups of such machines.
Today's coil winding equipment can operate at high rates, but this advantage cannot be fully realized because the existing winding techniques make it necessary to stop the rotation, after the winding of a coil group is completed, in order to carry out auxiliary operations.
There is known a method for manufacturing coils groups of an electric machine stator with the use of a stepped former. According to this method, wire is wound on each step of the former to produce a coil of a preset length, whereupon the wire is transferred from one step of the former to another by setting the winding head into advanced motion after a coil is completed. Finished coils are removed from the former to be received by a receiving mandrel. This method for the manufacture of coils groups of electric machine stators and an apparatus for effecting the method are disclosed in FRG Pat. No. 2,045,243, Cl. 21d 1, 51, of 1971.
The number of the former's steps is equal to that of coils in a coil group; the steps successively follow one another, but make up a single whole; the length of each step corresponds to that of a coil. Apparently, it is impossible to transfer finished coils in the course of the winding process, so all the coils of a coil group are removed at the same time after the wire is wound on all the steps of the former which by this time has been withdrawn from the winding zone and is in a position when the slots of the receiving mandrel are matched with the steps of the former. The term "winding zone" is to be understood as the space around the former, traversed by the rotating wire and confined lengthwise by the extreme positions of the wire along the axis of rotation.
According to the method under review, the winding of coils of a single coil group is a continuous process, yet the manufacture of coil groups is not continuous, which disadvantage strongly affects the overall efficiency.
The method is carried out with the aid of an apparatus (cf. the above-mentioned FRG Patent) comprising a horizontal winding head with a wire guide means. The winding head is movable in the axial direction and locked in with a rotary drive. There are also two stepped formers mounted on a bed so that they are rotatable in two mutually perpendicular planes and movable in the horizontal and vertical directions, for which purpose the stepped formers are provided with appropriate drive means.
To start the winding, one of the stepped formers is set in the horizontal position and introduced into the winding zone. Coil turns are moved and the wire is transferred from one step of the former to another by driving the winding head in the horizontal plane. In order to transfer coils to the receiving mandrel located under the fixture that carries the stepped formers, this fixture is rotated in the vertical plane to match the steps of the formers with respective slots of the receiving mandrel. The rotation of the stepped former in the vertical plane and the subsequent removal of the completed coil group are synchronized with the transfer of the winding head into the working position and the winding of a new coil group on the stepped former introduced into the winding zone by the same rotating fixture which withdraws the former with finished coils from the winding zone. This partially makes up for the disadvantage inherent in the design of the stepped former, by force of which finished coils can only be removed when the former is outside the winding zone. That notwithstanding, the rotation of the winding head has to be discontinued to rotate the fixture and move the winding head to the working position. Considering the mass of the winding head, it has of necessity be decelerated at the end of the winding process and accelerated again at the start of that process. With a small number of turns in a coil and with a limited time it takes to complete one coil group, the speed of rotation cannot reach a maximum possible level.
Thus the limitations of the method under review are due to the weak points in the design of the stepped former and other units of the apparatus which is used to carry out the method. The breakdown of the overall losses of time is as follows:
the time during which the winding head is at rest;
the time it takes to accelerate and decelerate the winding head;
the losses of time due to the inadequate rotation speed.
The foregoing method is realized with the aid of another machine disclosed in U.S. Pat. No. 3,714,973, Cl. 140-92, of 1973. The machine comprises a winding head with an axially movable wire guide means, a stepped former composed of concentric axially movable half-mandrels, and a receiving mandrel. The pins of the receiving mandrel are disposed in the gap between each pair of the half-mandrels whose outer surfaces make up a step of the coil former. The transfer of wire turns in the course of the winding process is effected by driving the wire guide means in the axial direction; the transfer of the wire from one step of the former to another is effected by an axial displacement of the pair of half-mandrels. The finished coils remain in the winding zone until all the steps of the former are filled, whereupon the former is driven in the axial direction to withdraw the coils from the winding zone and fit them over the pins of the receiving mandrel. The latter then turns so that its free pins reach the gap between the half-mandrels, whereupon the pair of half-mandrels, whose outer surfaces make up a step of the coil former, is moved to the winding zone, and the above sequence of events is repeated.
Here, as in the case discussed previously, the winding is discontinued after the completion of a coil group. Apart from the time it takes to wind the wire on the coil former, the total time of manufacturing of a coil group includes the time required to perform auxiliary operations, such as the transfer of the former from the winding zone, the transfer of the finished coils to the receiving mandrel and the rotation of the receiving mandrel. Clearly, this is not an optimum working cycle from the viewpoint of productivity.
Finally, the foregoing method for manufacturing coil groups of electric machines can be realized with the aid of a still another apparatus disclosed in USSR Inventor's Certificate No. 450,288, Cl. H 02 k 15/04, of 1974. This apparatus, which is the closest in design to the one of the present invention, comprises a winding head with a wire guide means, a stepped former, and a receiving mandrel. The winding head is installed in bearings secured in the bed of the apparatus; it is rotatable and kinematically coupled to a rotary drive. The former comprises two concentric mandrels mounted on a common rod extending through the winding head at the rotation axis. Both mandrels have the capability of independent axial motion and are shaped as cylindrical shells set upside down. The outer surfaces of the upturned cylindrical shells serve as the steps of the former, on which the wire is wound. These surfaces are bevelled, wherefore coil turns slide towards the receiving mandrel arranged under the stepped former and provided with receiving slots located opposite to the steps of the former. Introduced into the internal mandrel from the bottom is an axially movable crosspiece whose arms extend through slots provided in the walls of the mandrels. The cross-piece serves as a coil transfer mechanism which drives finished coils to the receiving mandrel; at the same time it serves to prevent the stepped former from rotation. The function of a switching device to transfer the wire from one step of the former to another is performed by the drive of the former's outer mandrel.
Wire is wound on the internal mandrel with the crosspiece introduced as for as it can go into the internal mandrel and with the external mandrel in its upper position. As the wire is wound on the bevelled surface of the internal mandrel, the turns slide onto the cylindrical portion of the surface, wherefrom they are received in the slots of the receiving mandrel. When the winding is over, there still are wire turns left on the cylindrical portion and not yet transferred to the receiving mandrel. The external mandrel is lowered to the winding zone so that its slots are fitted over the arms of the crosspiece which remains stationary. The wire is wound on the external mandrel as on the internal one so that the last turns of the wire remain on the cylindrical portion of the external mandrel. The crosspiece is then moved down and its arms, which serve as pushers, push the remaining wire turns of the internal and external coils onto the receiving mandrel. As the external mandrel and crosspiece are moved up, the foregoing sequence of events is repeated.
The movement of the crosspiece in the slots of the stepped former to the receiving mandrel and back is only possible when the winding head is at rest. The transfer of the external mandrel with the purpose of transferring the wire from the internal to the external step takes place slowly because of a considerable mass of that mandrel. Hence the rotation speed of the winding head has to be decreased in the course of this transfer, or has to be maintained at a constant relatively low level. These factors account for a low coil production rate.
Continuous winding of wire on the steps of the above former is impossible, since it is impossible to remove finished coils from that part of the former on which the winding is in progress.
It is impossible to increase the degree of bevelling of the mandrels' surfaces to enable all the coil turns slide down by gravity, because that would result in loosening the turns; the turns would thus lose contact with the surface of the former and the winding would be impossible. There is another important factor that has to be considered. The internal coil can be set in motion as the wire is wound on the external mandrel; yet for the external coil, forced motion is only possible when the former is moved outside the winding zone, towards the receiving mandrel, which means a stop of the winding process. Even if it were possible to remove wire turns from the steps of the former in a continuous manner, the winding process would unavoidably have to be stopped to remove the coils from the receiving mandrel or remove the receiving mandrel itself with the coils it contains.
Apart from reduced efficiency, frequent interruptions of the winding process lead to other disadvantages which are typical of all the foregoing apparatus for carrying out the known method for manufacturing coil groups. These disadvantages include increased power input due to frequent overloads on the motor while accelerating and decelerating the wire guide means, and reduced durability of the coil insulation, because the wire moves in jerks as the wire guide means is accelerated or decelerated.
It is an object of the present invention to eliminate the above disadvantages.
The invention essentially aims at providing a method for making coil groups of electric machines, which would make it possible to continuously wind the wire on the steps of a stepped coil former to produce coil groups containing any desired amount of coils and thus raise the efficiency of the coil making process and improve the quality of coils, while reducing power consumption; it is another object of the invention to provide a stepped former for carrying out the above method, wherein the mutual arrangement of the steps, the means for connecting concentric mandrel which make up the steps, and the coil transfer means would be such as to ensure continuous winding of wire on the steps of the former; it is a further object of the invention to provide an apparatus for manufacturing coil groups of electric machines, incorporating said stepped former which is interconnected with the winding head and a means for the transfer of wire from one step of the former to another so as to ensure continuous winding of the wire on the steps of the former by rotating the winding head at an increased speed.